Method for making a radio frequency component and component produced thereby

ABSTRACT

A method for making a radio frequency (RF) component includes forming a dielectric layer on a semiconductor substrate and forming and patterning a conductive layer on the dielectric layer to define the RF component. The dielectric layer may include SiN, the conductive layer may include aluminum, and the semiconductor substrate may include silicon, for example. At least one opening may be formed through the RF component at least to the semiconductor substrate. Moreover, the at least one opening may either extend into the semiconductor substrate or substantially terminate at a surface of the semiconductor substrate. The RF component may then be released from the semiconductor substrate by exposing the semiconductor substrate to an etchant passing through the at least one opening to the semiconductor substrate. Releasing the RF component may include exposing the semiconductor substrate to a dry etchant, such as XeF 2 , for example.

FIELD OF THE INVENTION

[0001] The present invention relates to the field of electroniccircuits, and, more particularly, to methods for forming electroniccircuits on dielectric layers.

BACKGROUND OF THE INVENTION

[0002] Radio frequency (RF) devices and integrated circuits (ICs), suchas inductors and capacitors, are well known for use intelecommunications applications. Many such devices and circuits are nowbeing formed using thin dielectric layers or “membranes” made out ofmaterials such as silicon nitride (SiN), for example. Such membraneshave been found to improve the electrical characteristics of RF circuitsmounted thereon. These membranes are typically formed on a substrate ofsuitable material, and the RF circuit is thereafter formed on themembrane which supports the RF circuit. The substrate provides supportfor the membrane during the patterning. Yet, capacitive coupling mayoccur between the substrate and the RF component, leading to deviceperformance degradation.

[0003] To overcome this limitation, the RF component may be separatedfrom the substrate. Prior art methods for removing the RF component fromthe substrate typically require etching a window through an oppositeside of the substrate to release the membrane. This so-called “backside”etching may include using hot potassium hydroxide (KOH) to etch asilicon substrate, for example, where the dielectric layer acts as anetch stop layer. One difficulty with backside etching is that itrequires careful double-sided alignment to make sure that the etchedarea corresponds with the membrane. Furthermore, due to thecorrosiveness of the KOH, any exposed portions of the substrate must beprotected from the etchant, e.g., by using a mask. Having to deposit andremove such a mask requires additional processing time and costs. Also,the etch rate of KOH is about 100 μm per hour. As a result, typical etchtimes for an eight inch wafer, for example, may be seven hours orgreater.

[0004] A prior art technique which addresses some of the difficultiesassociated with backside etching is disclosed in U.S. Pat. No. 5,853,601to Krishaswamy et al. entitled “Top-Via Etch Technique for FormingDielectric Membranes.” The patent is directed to methods for formingfilm bulk acoustic resonators (FBAR). The structure of an FBAR includesa substrate having a cavity on a surface thereof, a membrane on thesubstrate extending over the surface cavity, a first electrode on themembrane, a piezoelectric layer on the first membrane, and a secondelectrode layer on the piezoelectric layer. The method disclosed in thepatent includes forming vias or openings through the membrane layer andisotropically etching the substrate through the vias using a dry etchprocess including an SF₆ gas. While this method does address thedifficulty of backside alignment, it does not teach how to release theRF component from the substrate. Furthermore, the etching processdisclosed in the patent still requires a relatively long etch time dueto the nature of the reactive ion etchant. Such an etchant may alsodamage delicate circuit components of RF circuits like those describedabove.

SUMMARY OF THE INVENTION

[0005] In view of the foregoing background, it is therefore an object ofthe invention to provide a method for making a radio frequency (RF)component on a dielectric layer which alleviates the above notedproblems associated with the prior art.

[0006] This and other objects, features, and advantages in accordancewith the present invention are provided by a method for making an RFcomponent including forming a dielectric layer on a semiconductorsubstrate and forming and patterning a conductive layer on thedielectric layer to define the RF component. The dielectric layer mayinclude SiN, the conductive layer may include aluminum, and thesemiconductor substrate may include silicon, for example. At least oneopening may be formed through the RF component at least to thesemiconductor substrate. Moreover, the at least one opening may eitherextend into the semiconductor substrate or substantially terminate at asurface of the semiconductor substrate. The RF component may then bereleased from the semiconductor substrate by exposing the semiconductorsubstrate to an etchant passing through the at least one opening to thesemiconductor substrate.

[0007] Releasing the RF component may include exposing the semiconductorsubstrate to a dry etchant, such as XeF₂, for example. The at least oneopening may have a diameter in a range of about 0.5 to 20 μm. Also,forming the at least one opening may include forming a plurality ofopenings laterally adjacent to portions of the conductive layer with noopenings extending through the conductive layer. The plurality ofopenings may be formed in a predetermined pattern having substantiallyuniform spacing between adjacent openings, where the substantiallyuniform spacing is in a range of about 20 to about 200 μm, for example.

[0008] An RF component according to the invention is also provided. TheRF component may include a dielectric layer having opposing first andsecond major surfaces, the first surface being free from a semiconductorsubstrate, the dielectric layer having a plurality of openings extendingbetween the first and second opposing major surfaces. The RF componentmay also include a patterned conductive layer on the second majorsurface of the dielectric layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a cross-sectional diagram of a semiconductor substratehaving a dielectric layer formed thereon according to the presentinvention.

[0010]FIG. 2 is a cross-sectional diagram of the semiconductor substrateof FIG. 1 after the dielectric layer is patterned.

[0011]FIG. 3 is a cross-sectional diagram of the semiconductor substrateand patterned dielectric layer of FIG. 2 after the formation of aconductive layer thereon.

[0012]FIG. 4 is a cross-sectional diagram of the semiconductorsubstrate, patterned dielectric layer and conductive layer of FIG. 3after patterning of the conductive layer to thereby form an RFcomponent.

[0013]FIG. 5 is a top view showing the patterned conductive layer ofFIG. 4.

[0014]FIG. 6 is a cross-sectional view of the semiconductor substrateand patterned dielectric and conductive layers of FIG. 4 after formingopenings in the dielectric layer.

[0015]FIG. 7 is a top view showing the openings of FIG. 6.

[0016]FIG. 8 is a cross-sectional view of the semiconductor substrateand patterned dielectric and conductive layers for FIG. 6 illustratingreleasing of the patterned and conductive dielectric layers from thesemiconductor substrate.

[0017]FIG. 9 is a perspective view of an RF component according to thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The present invention will now be described more fullyhereinafter with reference to the accompanying drawings, in whichpreferred embodiments of the invention are shown. This invention may,however, be embodied in many different forms and should not be construedas limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thoseskilled in the art. Like numbers refer to like elements throughout.Also, the dimensions of layers and regions may be exaggerated in thefigures for greater clarity.

[0019] Referring now to the cross-sectional view of FIG. 1, a method formaking a radio frequency (RF) component is first described. The methodincludes forming a dielectric layer 11 on a semiconductor substrate 12.The semiconductor substrate 12 may include silicon and the dielectriclayer 11 may include SiN, for example. The dielectric layer 11 may beformed using conventional techniques known to those in the art (e.g.,chemical vapor deposition). The dielectric layer 11 may then bepatterned, again using conventional techniques, as shown in FIG. 2.

[0020] A conductive layer 13 is then formed using conventionaltechniques on the dielectric layer 11 (FIG. 3). The conductive layer 13may the be patterned to define an RF component 10, as shown in FIGS. 4and 5. Again, conventional lithographic and etch techniques known in theart may be used to pattern the conductive layer 13. The conductive layermay be aluminum, for example, although those of skill in the art willappreciate that other suitable conductors may be used as well. Theconductive layer 13 of a typical RF component may be patterned to be aninductor or a capacitor., for example, though other circuitconfigurations are also possible.

[0021] At least one opening 14 is then formed through the RF component10 at least to the semiconductor substrate 12, as seen in FIG. 6. In theillustrated example, six openings are formed in the RF component 10, ascan be seen in the top view of FIG. 7. Of course, any number of openings14 may be formed and the number selected will depend upon the size andshape of the component, the materials being used, etc., as will beappreciated by those of skill in the art. Specifically, the openings maysubstantially terminate at a surface of the semiconductor substrate 12,as shown in FIG. 6, or extend into the semiconductor substrate (notshown). The openings 14 may be formed using conventional lithographicand etch techniques, for example, as will be appreciated by those ofskill in the art.

[0022] The openings 14 are preferably formed laterally adjacent portionsof the conductive layer 13 with no openings extending through theconductive layer. Furthermore, the openings 14 may be formed in apredetermined pattern with substantially uniform spacing betweenadjacent openings. For example, the substantially uniform spacing may bein a range of about 20 to about 200 μm. Also, each of the openings 14may have a diameter in a range of 0.5 to 20 μm, for example.

[0023] The RF component 10 may then be released from the semiconductorsubstrate 12 by exposing the semiconductor substrate to an etchantpassing through the openings 14 to the semiconductor substrate, asillustrated in FIG. 8. The etchant may be a dry etchant, such as xenondifluoride (XeF₂) gas, for example. The XeF₂ may be used to etch siliconisotropically at a rate in a range of up to about 10 μm per minute, forexample. Furthermore, by appropriately spacing the predetermined patternof openings 14 for a given RF component, the semiconductor substrate 12only needs to be etched in small amounts in each of the defined regions.The combination of the increased etch rate of XeF₂ and appropriateselection of the predetermined pattern significantly reduces the timerequired to release the RF component 10 from the semiconductor substrate12 compared to prior art methods, as will be appreciated by those ofskill in the art. By way of example, a typical etch time to release anRF component from a silicon substrate according to the invention may beabout 20 minutes or less.

[0024] Additionally, XeF₂ is much less corrosive than prior artetchants, such as KOH and the like. As a result, the XeF₂ will havelittle effect on the RF component 10, so a mask need not be used toprotect the RF component. Avoiding such a masking step not only reducesthe complexity of manufacturing an RF component but also results insavings in time and costs. Additionally, if silicon, for example, isincluded in the conductive layer 13, the material (e.g., photoresist)used to define the pattern for the openings 14 would also serve toprotect any exposed silicon from being etched, which would also furtherprevent additional process steps and reduce production time. Thephotoresist material will also protect exposed portions of thesemiconductor substrate 12 from being unintentionally etched, as will beappreciated by those of skill in the art. Of course, those of skill inthe art will also appreciate that the above described method alsoobviates the need for backside etching, which again reduces processingcomplexity and costs.

[0025] A completed RF component 10 made as described above may be seenin the perspective view of FIG. 9. The RF component 10 includes adielectric layer 11 having opposing first and second major surfaces15,16, respectively. As can be seen, the first surface 15 is free fromthe semiconductor substrate 12. The dielectric layer 11 has a pluralityof openings 14 extending between the first and second opposing majorsurfaces 15, 16. The RF component 10 also includes a patternedconductive layer 13 on the second major surface of said dielectriclayer. The size, placement, and depth of the plurality of openings 14may be similar to those described above. Each opening 14 may also haverespective rounded over edges 17 adjacent the first and second majorsurfaces 15, 16 formed during etching of the openings 14, as will beappreciated by those of skill in the art.

[0026] Other devices and techniques using XeF₂ are disclosed inco-pending patent U.S. patent application Ser. No. 09/637,069, filedAug. 11, 2000, also assigned to present assignee, which is herebyincorporated herein in its entirety by reference. In addition, manymodifications and other embodiments of the invention will come to themind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is to be understood that the invention is not to belimited to the specific embodiments disclosed, and that othermodifications and embodiments are intended to be included within thescope of the appended claims.

1-28 (Canceled)
 29. A radio frequency (RF) component comprising: adielectric layer having opposing first and second major surfaces, thefirst surface being free from a semiconductor substrate, said dielectriclayer having a plurality of openings extending between the first andsecond opposing major surfaces; and a patterned conductive layer on thesecond major surface of said dielectric layer.
 30. The RF component ofclaiming 29 wherein said plurality of openings are arranged in apredetermined pattern.
 31. The RF component of claim 30 wherein thepredetermined pattern has substantially uniform spacing between adjacentopenings.
 32. The RF component of claim 1 wherein the substantiallyuniform spacing is in a range of about 20 to about 200 um.
 33. The RFcomponent of claim 9 wherein each opening has a diameter in a range ofabout 0.5 to 20 um.
 34. The RF component of claim 119 wherein eachopening has respective rounded over edges adjacent the first and secondmajor surfaces.
 35. The RF component of claim 29 wherein the pluralityof openings are laterally adjacent portions of the conductive layer withno openings extending through the conductive layer.